Re: [PATCH v5 0/8] perf: support specify vdso path in cmdline

[duchangbin <changbin.du@huawei.com>]

Hello, are there any more comments about this revision?

On Tue, Jul 02, 2024 at 12:18:29PM +0800, Changbin Du wrote:
> The vdso dumped from process memory (in buildid-cache) lacks debugging
> info. To annotate vdso symbols with source lines we need a debugging
> version.
> 
> For x86, we can find them from your local build as
> 'arch/x86/entry/vdso/vdso{32,64}.so.dbg'. Or they may resides in
> '/lib/modules/<version>/vdso/vdso{32,64}.so' on Ubuntu. But notice that the
> builid has to match. 
> 
> If user doesn't specify the path, perf will search them internally as long
> as vmlinux when recording samples. The searched debugging vdso will add to
> buildid cache.
> 
> Below samples are captured on my local build kernel. perf succesfully
> find debugging version vdso and we can annotate with source without
> specifying vdso path.
> 
> $ sudo perf record -a
> $ sudo perf report --objdump=llvm-objdump
> 
> Samples: 17K of event 'cycles:P', 4000 Hz, Event count (approx.): 1760
> __vdso_clock_gettime  /work/linux-host/arch/x86/entry/vdso/vdso64.so.d
> Percent│       movq    -48(%rbp),%rsi
>        │       testq   %rax,%rax
>        │     ;               return vread_hvclock();
>        │       movq    %rax,%rdx
>        │     ;               if (unlikely(!vdso_cycles_ok(cycles)))
>        │     ↑ js      eb
>        │     ↑ jmp     74
>        │     ;               ts->tv_sec = vdso_ts->sec;
>   0.02 │147:   leaq    2(%rbx),%rax
>        │       shlq    $4, %rax
>        │       addq    %r10,%rax
>        │     ;               while ((seq = READ_ONCE(vd->seq)) & 1) {
>   9.38 │152:   movl    (%r10),%ecx
> 
> When doing cross platform analysis, we need to specify the vdso path if
> we are interested in its symbols. At most two vdso can be given. Also you
> can pack your buildid cache with perf-archive if the debugging vdso can be
> found on the sampled machine.
> 
> $ sudo perf report --objdump=llvm-objdump \
>       --vdso arch/x86/entry/vdso/vdso64.so.dbg,arch/x86/entry/vdso/vdso32.so.dbg
> 
> I also improved perf-buildid-cache command recognize vdso when adding files, then
> place it at correct place.
> 
> v5:
>   - Searching the vdso in record stage instead of report. So the debugging
>     vdso will be in build-id cache. This is friendly for cross-machine analysis.
>   - Improve perf-buildid-cache command recognize vdso when adding files
> v4:
>   - split the refactoring from the actual change.
> v3:
>   - update documentation.
> v2:
>   - now search vdso automatically as long as vmlinux, as suggested by Adrian.
>   - remove change 'prefer symsrc_filename for filename'.
> 
> 
> Changbin Du (8):
>   perf: support specify vdso path in cmdline
>   perf: disasm: refactor function dso__disassemble_filename
>   perf: disasm: use build_id_path if fallback failed
>   perf: build-id: name debugging vdso as "debug"
>   perf: symbol: generalize vmlinux path searching
>   perf: build-id: try to search debugging vdso and add to cache
>   perf: disasm: prefer debugging files in build-id cache
>   perf buildid-cache: recognize vdso when adding files
> 
>  tools/perf/Documentation/perf-annotate.txt |   3 +
>  tools/perf/Documentation/perf-c2c.txt      |   3 +
>  tools/perf/Documentation/perf-inject.txt   |   3 +
>  tools/perf/Documentation/perf-report.txt   |   3 +
>  tools/perf/Documentation/perf-script.txt   |   3 +
>  tools/perf/Documentation/perf-top.txt      |   3 +
>  tools/perf/builtin-annotate.c              |   2 +
>  tools/perf/builtin-buildid-cache.c         |  26 ++-
>  tools/perf/builtin-c2c.c                   |   2 +
>  tools/perf/builtin-inject.c                |   2 +
>  tools/perf/builtin-report.c                |   2 +
>  tools/perf/builtin-script.c                |   2 +
>  tools/perf/builtin-top.c                   |   2 +
>  tools/perf/util/build-id.c                 |  57 +++++-
>  tools/perf/util/disasm.c                   | 131 ++++++++-----
>  tools/perf/util/machine.c                  |   4 +-
>  tools/perf/util/symbol.c                   | 209 ++++++++++++++++-----
>  tools/perf/util/symbol.h                   |   9 +-
>  tools/perf/util/symbol_conf.h              |   5 +
>  19 files changed, 359 insertions(+), 112 deletions(-)
> 
> -- 
> 2.34.1
> 

-- 
Cheers,
Changbin Du